Fiber reinforced ceramic matrix composite (FRCMC) materials have recently been employed to make structural components for aircraft. Specifically, these components have been used as so called "hot structures", i.e. portions of the aircraft which must withstand high temperatures. FRCMC parts have fibers of various types and lengths disposed throughout a ceramic matrix formed from a pre-ceramic resin. Such parts have advantages over those formed of organic composite materials. For example, organic composites would tend to degrade in high temperature environments such as described above. While organic composites will burn readily, FRCMC, being a ceramic, withstands heat that can destroy even metals. A FRCMC material can withstand continuous temperatures up to about 1000.degree. F., cyclical temperatures up to about 2000.degree. F., and short-term exposure to temperatures up to about 3500.degree. F. FRCMC structures also have advantages over those made from monolithic ceramic materials. Although monolithic ceramic structures can withstand high temperatures, they tend to be porous, delicate, and brittle. These parts are easily broken or cracked when impacted, or otherwise subjected to even moderate forces. Parts made from FRCMC materials, on the other hand, exhibit an increased ductility. Ductility for the purposes of the present invention is defined as the amount of strain a sample of the FRCMC material can withstand before fracturing. Increasing the ductility of a part makes it less susceptible to the fracturing associated with monolithic ceramic parts.
FRCMC materials have in the past been generally restricted to structural components designed to withstand high temperature environments. Other than its inherent heat resistance, no other significant demand is made on the parts employed in these types of applications. However, FRCMC materials could be useful in many other applications where certain additional physical characteristics would be required. For example, FRCMC materials could be employed in mechanical parts which are intended to be in sliding contact with other parts. In such a case it would be desirable that the FRCMC material exhibit high ductility and erosion resistance, and a low coefficient of friction. In other applications, such as in the friction components of brakes and clutches, the same erosion resistance would be desired, but the FRCMC material would have to exhibit a high coefficient of friction to prevent slipping. In the case of structural components, a FRCMC part may not only be required to withstand high temperatures, but also abrasive environments. This calls for a FRCMC material which is hard enough to survive in these abrasive environments.
Accordingly, there is a need for parts made of FRCMC materials that exhibit a desired ductility, hardness (i.e., erosion resistance) and/or coefficient of friction required for a particular application.
It is therefore an object of the present invention to provide FRCMC parts which exhibit a desired degree of ductility.
It is another object of the present invention to provide FRCMC parts which exhibit a desired degree of hardness, or a desired coefficient of friction, or both.
These and other objects of the present invention will become apparent throughout the description thereof which now follows.